This invention relates to an oxygen absorbent composition consisting essentially of (a) an oxygen absorbent comprising a dithionite as a main component and (b) a fiber component which is usable for preserving foodstuffs, etc., and particularly relates to an oxygen absorbent capable of being tableted.
In order to preserve foodstuffs, such as vegetable, fish, shellfish, meats, processed foodstuffs, such as potato chips, cakes, peanuts, etc., and so on, it is necessary to prevent the foodstuffs from getting moldy and from putrefying. Prior art methods have used freezer storage, cold storage, vacuum packaging and replacing the gas present in the inner part of packaging by an inert gas for preventing foodstuffs from getting moldy and putrefying. Additives, such as antioxidant, have been used for preserving foodstuffs. Recently, governments have started to regulate the use of additives for food, since it is realized that some additives are injurious to humans. The freezer storage method requires large-scale apparatus and complicated operation, so the freezer storage method is costly.
Molds or eumycetes, bacterias and higher organisms such as insects tend to disturb preservation of foodstuffs. These mold eumycetes, bacterias and insects live and grow in the presence of oxygen and cause putrefaction and change in quality of foodstuffs.
Therefore, if oxygen can be selectively removed from the atmosphere in which the foodstuffs are packed, the problems of putrefaction and change in quality of foodstuffs can be overcome, and it will become possible to preserve foodstuffs for a long time.
Attempts for producing such an oxygen absorbent have previously been made.
A prior art oxygen absorbent comprising a dithionite as a main component is known. For example, Japanese Patent Application Nos. 144418/1975, 3539/1976 and 27792/1976 and U.S. Ser. No. 760,817 filed on Jan. 19, 1977 now U.S. Pat. No. 4,104,192 issued Aug. 1, 1978 (all these patent applications were assigned to the assignee of this invention.) disclose an oxygen absorbent comprising a dithionite, an alkaline material, water (including water of hydration or water of crystallization) or an alcohol and an adsorbent, such as activated carbon. In the oxygen absorbent, the alkaline material absorbs SO.sub.2 formed by reacting the dithionite with oxygen; and the adsorbent, such as activated carbon acts as a deodorizer. When an alcohol is used in place of water, an oxygen absorbent having a slow absorbing rate is obtained. When an oxygen absorbent is applied to water-containing foodstuffs, that is, when compounds having water of crystallization is used, or when the absorbent is used with water-containing foodstuffs, or water-generating materials, free water or an alcohol is not necessarily contained in the absorbent, because nearly saturated water vapor is present in a closed system containing these materials.
The known oxygen absorbents are all powdery and in use a permeable paper bag is filled with the absorbent. The present inventors found that the known oxygen absorbents have the following shortcomings:
(a) In using the oxygen absorbent with foodstuffs, if the paper bag is broken, the absorbent powder scatters and there is possibility of contaminating the foodstuffs.
(b) When the absorbent is used with foodstuffs in an atmosphere containing much water vapor or much moisture, the paper bag is likely to be weakened and broken, whereby the use of the absorbent is much limited.
(c) When the absorbent is used with foodstuffs having oils on the surface thereof, for example potato chips, the paper bag tends to be weakened and broken by action of the oils, whereby the use of the absorbent is much limited.
(d) In case of storing a large amount of foodstuffs by removing oxygen in the atmosphere of the foodstuffs by forced contact of the atmosphere with a large amount of an oxygen absorbent, heat generated through the deoxygenation reaction accumulates, because the absorbent is powdery, and there is risk that the vapor generated by accumulation of heat and gas generated by decomposition of the components will impair the foodstuffs.
(e) Since the powdery absorbent has small bulk specific gravity--that is, it is bulky, a large bag is required for packing the absorbent. In other words, a large volume of the absorbent is required for absorbing a definite amount of oxygen. This is uneconomical.
Therefore, it is necessary to tablet the oxygen absorbent for overcoming such shortcomings. The tableting must not impair the deoxygenating action of the dithionite.
In general, tableting process are of two types; dry and wet.
There are two kinds of wet process, as follows:
A. (a) powderizing, (b) mixing the powder with water, (c) granulating, (d) drying, and (e) tableting.
B. (a) powderizing, (b) mixing the powder with water, (c) tableting, and (d) drying.
There are two kinds of dry process, as follows:
C. (a) powderizing, (b) slug-tableting, (c) granulating, (d) sieving, and (e) tableting.
D. (a) powderizing and (b) tableting.
When a large amount of water is added to the oxygen absorbent composed of a dithionite, or when the oxygen absorbent is forcedly contacted with air or is dried, the inherent action or the oxygen-absorbing ability of the oxygen absorbent is impaired. Therefore, tableting of the oxygen absorbent by the wet processes is not preferred.
Therefore, in order to tablet the oxygen absorbent containing a dithionite, tableting of the oxygen absorbent by the dry process is preferred. Also, since the oxygen absorbent is chemically active, it is preferred to simplify the steps for tableting the powder. In the dry tableting process, whether the powder can be tableted and the selection of appropriate binders are the problems. In fact, when the known powdery oxygen absorbent containing a dithionite is tableted without using any binder, tablets having the strength required to resist the handling can not be obtained.
For both the dry and wet tableting processes, the binders employed for tableting the powdery oxygen absorbent include, for example, solid binder, such as carboxymethyl cellulose (CMC), potash alum, sodium aliginate, polyvinyl alcohol powder, starch, gum arabic, bentonite, zeolite, gelatin, sodium polyphosphate, sodium metaphosphate, sodium borate, rosin, powderous alcohols and the like; and liquid binders, such as monohydric alcohol, water, ethylene glycol, propylene glycol, diethylene glycol, water-glass, glycerine, liquid paraffins, oils, high molecular alcohols and the like.
However, the present inventors found that, even in case of tableting the oxygen absorbent containing a dithionite using any of these binders, the good results can not be obtained. That is, in case of tableting the absorbent using any of these binders, tablets having a hardness of more than 5-6 kg required to resist handling the tablet can not be obtained. Even if a tablet having such handling strength is obtained, the resulting tablet is fragile due to capping phenomenon, and is not practical. The edge of the tablet so obtained is likely to be chipped and the tablet is not glossy. In the tableting by continuous tableting machine, the powder compressed on the mold forms a membrane which adheres to the surface of the mold, and the membrane hinders the continuous tableting operation. Therefore, the known binders are not usable for tableting the oxygen absorbent containing a dithionite.